The invention relates to a new process for the production of .beta.-carbolines from the corresponding 1,2,3,4-tetrahydro-.beta.-carbolines by dehydro-genation.
Processes for the production of .beta.-carbolines from 1,2,3,4-tetrahydro-.beta.-carbolines have been known for a long time (e.g., see GB PS No. 975,835). According to the latter, dehydrogenation is carried out at an elevated temperature in the 140.degree.-150.degree. C. range in a suitable solvent such as dimethylformamide in the presence of selenium, sulfur or chloranil. Sulfur/dimethylsulfoxide can also be successfully used (Heterocycles, 1983 (20), 1293). However, these methods have the disadvantage that the yields leave much to be desired due to a relatively drastic treatment of the starting material and the subsequent separation of by-products.